The present invention relates to an electrophotographic image forming apparatus for forming an image on a transfer sheet of a copier or printer, and more particularly relates to an image forming apparatus to which processing components for image formation including an image carrier are provided in the form of one unit.
Many methods and apparatus for obtaining color images using an electrophotographic method have been proposed. For example, as indicated in Japanese Patent Publication Open to Public Inspection No. 100770/1986, there is a method in which latent images are formed on a photosensitive drum, which is an image forming unit. Depending on the number of separated colors of an original image, the latent images are transferred onto a transfer drum after being developed so as to form a multi-color image on the transfer drum, and then they are transferred onto a transfer sheet so as to obtain a color copy. An apparatus using this method requires a transfer drum, the diameter of which is large enough to transfer one sheet of image onto the peripheral surface thereof, in addition to the photosensitive drum. The size of the apparatus is inevitably large and the structure is complicated.
Furthermore, for example, as indicated in Japanese Patent Publication Open to Public Inspection No. 149972/1986, there is a method in which latent images are formed and developed on a photoreceptor drum, depending on the number of separated colors of an original image. The latent images are transferred onto a transfer sheet when they are developed so as to obtain a multi-color copy. It is difficult in this method to registrate numerous color images with high accuracy, and color copies of good quality can not be obtained.
Furthermore, there is a method in which latent images are formed on a photosensitive drum, depending on the number of separated colors of an original image, and developed by color toners, repeatedly. In this matter, color toner images are registered on the photosensitive drum and transferred so as to form a color image. This basic process of multi-color image forming is indicated in Japanese Patent Publication Open to Public Inspection Nos. 75850/1985, 76766/1985, 95456/1985, 95458/1985, and 158475/1985 by the applicants of this application.
A multi-color image forming apparatus for forming color images by registration includes a plurality of developing units containing different color toners installed around the photosensitive drum. Latent images on the photosensitive drum are developed generally by rotating the photosensitive drum several times so as to form color images.
In an image forming apparatus, such as a monochromatic color analog copier using the electrophotographic method or a copier or printer using a semiconductor laser LED scanning system, an apparatus has been proposed in which a part of the image forming means is provided as a cartridge unit. The cartridge unit is used for replenishing or replacing various photoconductors of limited durability, developer carriers, cleaning materials, and developing toners when they are exhausted, whereby the integrated unit of the essential units of these image forming means is removed for maintenance or replacement. Various structures have been proposed, for example, configuring the feed path of a transfer sheet whereon an image is formed by the image forming means to be opened so that the transfer can be easily removed for clearing a jam.
A typical structure in which a photosensitive drum, developing unit, and cleaner are integrally mounted on a support member so that they can be removed from the main unit and each unit can be easily replaced or repaired is indicated in Japanese Patent Publication No. 54392/1983. A structure in which the essential units of the image forming means are integrated and not reused is indicated in Japanese Patent Publication Open to Public Inspection No. 154255/1982 Likewise a printer structure in which a non-reusable cartridge is used such that latent images are formed on a photosensitive drum by the dot, exposure scanning of a semiconductor laser is indicated in Japanese Patent Publication Open to Public Inspection No. 147366/1984.
Furthermore, the aforementioned publication indicates a structure in which the upper frame of the divided structure is opened so as to open the transfer sheet feed path, whereby the transfer sheet can be easily removed in the case of jamming. Japanese Patent Publication Open to Public Inspection No. 154255/1982 mentioned above indicates a structure in which a non-reusable process cartridge is mounted on the upper frame of the bisecting structure so that it can be replaced, increasing operability of cartridge replacement and the ease of jam clearance. A structure in which priority is given to the ease of process cartridge replacement, such as a replenishing toner cartridge or a collected toner cleaning cartridge, is indicated in Japanese Patent Publication Open to Public Inspection No. 1161/1983. In it particularly noted that a process cartridge, is mounted on the lower frame so as to improve the operability of maintenance.
A structure in which a vertical type of the aforementioned structure is used so as to improve the same directional operation and jam clearance is indicated in Japanese Patent Publication Open to Public Inspection Nos. 244058/1988, 244059/1988, 244064/1988, and 179168/1989.
However, a compact printer having a process cartridge, which comprises a developing unit and an image carrying member, which can be easily provided to or removed from the apparatus body, which is free of leakage or spilling of toner or developer from the developing unit when it is provided to or removed from the apparatus body, and which is free of such problems during clearance of a jammed transfer sheet, has not yet been proposed.
A proposal in which when the upper frame of a printer of bisecting structure is open, a process cartridge mounted on the upper frame is always kept horizontal so as to prevent waste toner from spilling, is indicated in Japanese Patent Publication Open to Public Inspection No. 190961/1983. Although this structure allows the cartridge to be easily mounted or a jam to be easily cleared, problems such as spilling or leakage of toner caused when the cartridge is mounted, a jam is cleared, or a replacement operation is performed for maintenance, have not been solved.
In Japanese Patent Publication Open to Public Inspection No. 72159/1983 is disclosed a printer having a bisecting structure wherein a jam can be easily cleared, and a non-reusable cartridge is mounted on the upper frame. In Japanese Patent Publication Open to Public Inspection No. 1161/1983, a replenishing or collected toner can be easily replaced; a process cartridge is mounted on the lower frame; and the process cartridge of a developing unit, cleaning unit, and photosensitive drum can be raised for clearing a jam. However, the operability of the process cartridge replacement conflicts with the ease of jam clearance. Furthermore, in these process cartridges, since the developing unit and the cleaning unit are mounted at the bottom across the paper feed path from the transfer electrode, toner spills from the developing unit or the cleaning unit cause the inside of the apparatus or the transfer paper to become soiled. This occurs if the process cartridge is positively sealed when the process cartridge is replaced or external vibration or shock is applied to the apparatus body.
The printer indicated in Japanese Utility Model Laid Open to Public Inspection No. 195357/1988 contains a process cartridge and forms a flat paper feed path at the upper part. However, there are some restrictions on the feed path from the transfer sheet separation unit of the photosensitive drum to the fixing unit, and problems of the feed unit have not been solved. Furthermore, the printer lacks ease of jam clearance when it is opened, such that compactness is restricted due to the upstanding stack paper feeding structure, and the opening angle of the upper frame. Therefore, the printer is not an apparatus which is superior in operability.
As to a color image forming unit, as described previously, a belt type image forming unit wherein a photoconductor is coated or deposited on a flexible belt has been proposed. For example, in Japanese Patent Publication Open to Public Inspection No. 55573/1991 by the applicant of this application a photosensitive drum is provided by a photoconductor which is coated or deposited on the peripheral surface of the drum. The shape of the belt type of image forming unit (hereinafter called a photosensitive belt) is determined by stretching the photosensitive belt between between rotating rollers, including a drive roller. The belt type of image forming unit is effective from the viewpoint of compactness, using space effectively. Since the photosensitive belt can move around a small curvature, defective separation of a transfer sheet can be prevented by separating the transfer sheet using the curvature of a rotating roller with a small diameter.
In a color image forming apparatus using such a photosensitive belt, image forming means such as a charging means, an image exposure means, a plurality of developing units, and a cleaning means are installed mainly below the lower surface of the outer peripheral surface of the photosensitive belt. Those components which make up the and those image forming means are integrated in a process cartridge together with the photosensitive belt, and the process cartridge can be freely provided to or dismounted from the apparatus body.
A transfer sheet whereon a color toner image is transferred is ejected onto a paper ejection tray installed on the top of the apparatus with the copy side down. Therefore, the necessary area of a place where the apparatus is to be installed, is small.
A structure in which problems of paper feed and jam clearance are solved by using a compact cartridge and the same side operation is possible, as indicated in Japanese Patent Publication Open to Public Inspection Nos. 40850/1989 and 244059/1988.
A concept of control for outputting an indication showing the exhaustion of a process cartridge or the expiration of the life of a photoconductor, is indicated in Japanese Patent Publication Open to Public Inspection No. 85763/1988. However, an image forming apparatus, which is compact and easy to operate and satisfies all the requirements such as easy jam clearance, no spilling of toner during cartridge operations, easy cartridge replacement, and all operations available from one side via the front of the apparatus body, has not been proposed. A concept to provide a protective cover in order to prevent a photoreceptor from being damaged when it is attached to and detached from the apparatus, has been disclosed in the official gazette of Japanese Patent Publication Open to Public Inspection 211181/1982. Likewise, and a concept to open and close a cover being linked with the motion of opening when the apparatus is bisected, has been disclosed in the official gazette of Japanese Patent Publication Open to Public Inspection 181062/1983. However, the aforementioned structure is not suitable for the opening and closing motion of the cover in accordance with the position of the cartridge. The opening is formed on the edge of the transfer section, so that the opening is not adequate to be used for maintenance.
In the case of a color image forming apparatus, a plurality of developing units and a plurality of toner supplying units are provided. Therefore, the structure of the image forming section is complicated, so that it is very difficult to inspect, replace, or replenish each component for processing use.
In order to solve the aforementioned problem, the image forming apparatus is structured in such a manner that at least a photoreceptor and a cleaning unit are integrally provided in a cartridge; or a photoreceptor, a developing unit and a cleaning unit are integrally provided in a cartridge, so that the aforementioned cartridge can be easily removed from the apparatus body.
In the case of the aforementioned cartridge, most of the photosensitive surface of the photoreceptor is covered. However, the exposure and transfer zone are not covered, so that when the cartridge is located inside the apparatus body, it may be soiled with dust, and when the cartridge is taken out of the apparatus, there is a possibility that the exposure and transfer region may be soiled or damaged by hands or other objects.
It is a primary object of the present invention to provide an image forming apparatus characterized in that: articles of consumption can be easily replaced; components can be easily maintained and replaced; jam clearance can be easily conducted; and the photoreceptor can be protected during the operation.
The second object of the present invention is to provide an image forming apparatus characterized in that the exposure and transfer zone of the photoreceptor are always covered except when the image formation process operation is being conducted so that the photosensitive surface of the photoreceptor can be protected.